The new head of civil rights at the Education Department has reopened a seven-year-old case brought by a Zionist group against Rutgers University, saying the Obama administration, in closing the case, ignored evidence that suggested the school allowed a hostile environment for Jewish students.

The move by Kenneth L. Marcus, the assistant secretary of education for civil rights and a longtime opponent of Palestinian rights causes, signaled a significant policy shift on civil rights enforcement — and injected federal authority in the contentious fights over Israel that have divided campuses across the country. It also put the weight of the federal government behind a definition of anti-Semitism that targets opponents of Zionism, and it explicitly defines Judaism as not only a religion but also an ethnic origin.

In a letter to the Zionist Organization of America, obtained by The New York Times, Mr. Marcus said he would vacate a 2014 decision by the Obama administration and re-examine the conservative Jewish group's cause not as a case of religious freedom but as possible discrimination against an ethnic group.

In so doing, the Education Department embraced Judaism as an ethnicity and adopted a hotly contested definition of anti-Semitism that included "denying the Jewish people the right to self-determination" by, for example, "claiming that the existence of a State of Israel is a racist endeavor" and "applying double standards by requiring of" Israel "a behavior not expected or demanded of any other democratic nation."

In effect, Arab-American activists say, the government is declaring the Palestinian cause anti-Semitic.

Liz Hill, a spokeswoman for the Education Department, said that although the Office for Civil Rights does not have jurisdiction over religious discrimination, the office "aggressively enforces" civil rights law, "which prohibits discrimination on the basis of race, ethnicity or national origin."

Education Secretary Betsy DeVos "has made clear that O.C.R. will look at the specific facts of each case and make determinations accordingly," Ms. Hill said. "The facts in this case, many of which were disregarded by the previous administration, are troubling."

A spokeswoman for Rutgers said the university had not received official notification from the Education Department yet, but "as always, we would certainly cooperate with the Department of Education should they decide to review the decision." The letter is dated Aug. 27 but received no public notice.

When the initial complaint was filed in April 2011, the school had been trying to address brewing tensions over the B.D.S. movement — which advocates boycotting, divesting from and sanctioning Israel — that was roiling college campuses.

That month, the school hosted Omar Barghouti, a founding member of the Palestinian Campaign for the Academic and Cultural Boycott of Israel, and after his speech, in which he called for the university to distance itself from Israel, the school issued a statement assuring the college's Hillel group that it would not, according to published reports.

And when the complaint was filed, a spokesman told the New Jersey Jewish News that the claims in the complaint by the Zionist Organization of America were "contrary to the true values of Rutgers University and are not supported by the facts."

Mr. Marcus, who was confirmed in June, was tapped to lead the Office for Civil Rights from his job leading the Louis D. Brandeis Center for Human Rights Under Law, a nonprofit advocacy organization that Mr. Marcus used to pressure campuses to squelch anti-Israel speech and activities.

The organization advocated revocation of federal funding from Middle East studies programs that are said to have an anti-Israel slant, and it urged colleges and universities to discipline students who are part of the B.D.S. movement.

When Mr. Marcus was nominated, Palestinian and human rights organizations protested his confirmation on the grounds that he would use his position at the Education Department to further his pro-Israel cause, and that first on his list would be pushing to adopt a definition anti-Semitism to target schools for civil rights violations. Middle Eastern studies programs at universities around the country have braced for action from Washington against perceived bias.

"This is exactly what we feared would happen — he has a long track record of pressuring universities and government bodies to trample on free speech," said Rahul Saksena, senior staff attorney at Palestine Legal, a Palestinian rights group. "You would think that the O.C.R. would have their hands full these days, and instead they're using their limited resources" to reopen a case "that the Education Department spent years investigating, and had been closed."

Mr. Marcus conceded that his department did not have the authority to weigh in on religious or political disputes. But he made the case that the Rutgers case is neither.

"An individual's pro-Israel viewpoint itself — or, for that matter, any viewpoint on the policies of the State of Israel, the Israeli-Palestinian conflict or related issues — is not protected by" federal civil rights law, he wrote. However, he added, "discrimination on the basis of actual or perceived shared ancestry or ethnic characteristics — which may include discrimination against Jewish or Muslim students — is."

Mr. Marcus's decision took current and former investigators at the Education Department by surprise, as Ms. DeVos has gone to great lengths to limit civil rights enforcement to stringent interpretations of federal law.

But in a previous stint leading the Office for Civil Rights, Mr. Marcus indicated that he was willing to interpret the law more broadly. In 2004, he issued a guidance letter telling schools that the department would include in its enforcement "national origin discrimination, regardless of whether the groups targeted for discrimination also exhibit religious characteristics."

The Zionist Organization of America called the reopening of the case a "groundbreaking decision."

In a statement, the organization's national president, Morton A. Klein, and Susan B. Tuchman, the director of its Center for Law and Justice, emphasized that Mr. Marcus's notification that the Education Department had adopted the expansive definition of anti-Semitism was particularly noteworthy.

"It took a leader like Kenneth Marcus to finally decide the ZOA's appeal and to also make it clear that O.C.R. will finally be using a definition of anti-Semitism that makes sense and that reflects how anti-Semitism is so frequently expressed today, particularly on our college campuses," they wrote. "Hate groups like Students for Justice in Palestine try to convince others that their attacks on Zionism and Israel are legitimate political discourse. But as the State Department definition of anti-Semitism recognizes, these attacks are often a mask for Jew-hatred, plain and simple."

Mr. Marcus informed ZOA that he would specifically be reviewing one of the three allegations made in its 2011 complaint, which said that a liberal, pro-Palestinian group, Belief Awareness Knowledge and Action, imposed an admissions fee on Jewish and pro-Israeli students who attended an event called "Never Again for Anyone." The Zionist group said an email proved that an organizer wrote that the group began charging only after it observed "150 Zionists" who "just showed up."

But according to an account from Palestine Legal, fees were charged for the event only after Rutgers Hillel, a local synagogue, and other Jewish groups sent alerts to mobilize their members to protest the event. The group said that pro-Israel protesters physically assaulted event volunteers and called them "towel heads" and "suicide bombers," and that a Jewish volunteer was called a "traitor."

The organizers — who were not students — said they were forced to charge a last-minute fee to cover costs mandated by the university, including an increased price to rent the space and to cover security to manage the protests.

In dismissing the case in 2014, the Education Department determined that the host of the event advertised a $5 to $20 donation, and began charging last-minute fees because the event drew more attendees than anticipated, including many nonstudents.

In their findings letter, department investigators wrote that they had discovered no evidence that Jewish and non-Jewish attendees were selectively charged fees. They said the email that said "150 Zionists" had shown up — which was presented as evidence of the intended discrimination — was heavily redacted, and they could not verify whether that information was credible. The department said it determined from witness statements that all attendees were required to pay for the event if they were not a volunteer. The department also found that Rutgers promptly investigated complaints of bias filed by students.

"Regardless of whether or not it was appropriate to begin charging the admissions fee, O.C.R. did not find sufficient evidence to substantiate that any individuals were treated differently, based on national origin, with respect to imposition of the admissions fee," the findings letter said.

The Zionist group appealed the finding.

In his letter, Mr. Marcus wrote that the email was sufficient enough for further investigation.

"In other words, the visual perception of the presence of '150 Zionists' referenced in the email could have been rooted in a perception of Jewish ancestry or ethnic characteristics common to the group," Mr. Marcus wrote to the group. "In cases such as this, it is important to determine whether terms such as 'Zionist' are actually code for 'Jewish.'"

Mr. Marcus's confirmation was opposed by more than 60 civil rights organizations who expressed concern that his view of civil rights, and whose should take priority, was too narrow.

Mr. Marcus supports scaled-back protections for transgender students and rejects that policies could have "disparate impact" on racial and other groups, and his organization has filed amicus briefs challenging affirmative action.

"Mr. Marcus expressed significant concern for a student who might be subject to harassment based on religion, but expressed no similar concern about a student's right to be free from harassment based on their sexual orientation or gender identity," the organizations, part of the Leadership Conference on Civil and Human Rights, wrote of his nomination. "Mr. Marcus has sought to use the complaint process to chill a particular political point of view, rather than address unlawful discrimination."